Photometer



Patented Nov. 13, 1951 UNITED STATES PATENT OFFICE PHO'IOMETER Gordon F.Laing, Delavan, Wis.

Application March 31, 1948, Serial No. 18,271

I (01.- ss-zs) film of any speed.

A feature of the invention is a standard light source comprising afluorescent screen activated by radioactive material.

A further feature is a photometer employing a standard light source asdescribed in the foregoing, wherein the fluorescent screen and theradioactive material, radium or the like, are in operative relation toeach other only while the device is in use.

These and other features of the invention will be fully described in theensuing specification, reference being had to the accompanying drawing,in which Fig. 1 is a back view of a photometer embodying the invention;

Fig. 2 is a side view of the same;

Fig. 3 is a rear view of the device with the back cover removed;

Fig. 4 is a section on the line 4-4, Fig. 1;

Figs. 5 and 6 correspond generally to Figs. 3 and. 4, respectively, andshow a modified form of the invention; and

Fig. '7 is an enlarged view of certain parts shown in Fig. 4.

Referring to the drawing, the cup shaped body l0, having the integrallyformed eye piece II, may be molded from a suitable plastic material. Theeye piece II is non-concentric with the body H), as can be seen fromFigs. 1 and 2. The lens I2 is mounted in the eye piece II, as seen inFig. 4. The scale l3 carried by the body In is calibrated in accordancewith various film speeds.

The ring 14 may also be molded from plastic material and is rotatable onthe body H! for the purpose of adjusting the index IS with respect tothe scale Is. The ring should fit rather tightly so that it will stay inadjusted position. If desired, a suitable friction device may beinterposed between the ring and body. The scale l5 carried on the ringis calibrated for the different exposure times in accordance with whichcamera shutters are commonly adapted 'to operate.

Claims.

means of screws [8 and [9, as shown in Fig. 3.

The reference numeral 20 indicates a shoulder stud which is secured tothe center of the disc I! by riveting or staking.

The back or cover 2| may be molded of plastic material like the body 10and ring I4 and is rotatable with respect to these parts. It is held inplace on the body II] by the screw 22 which is threaded into the stud20. The scale 23 carried by the cover 2! is calibrated in accordancewith a common system of stops or diaphragm apertures. The cover shouldhave a rather easy flt so that itcan be adjusted without disturbing theadjustment of the ring M.

The plastic material from which the body HI, ring l4, and cover 2| aremade may be material such as Bakelite which is opaque to light. Thewindow 25 in the cover 2|, shown in Figs. 1 and 3, is made oftransparent material such as glass or a plastic known as Lucite and maybe secured in place by a suitable cement. As an al-' ternative, thecover 2| may be molded throughout of transparent material such as Luciteplastic and painted inside and out, except for the area of window '25,with black paint. The window is thus formed integrally with the rest ofthe cover and a stronger structure is obtained.

Directly opposite the lens E2 the disc I1 has two small circularopenings 2'! and 28, shown in Figs. 4 and 7. Theopening 21 is covered bya green light filter 29 which may be made, for example, of severallayers of green cellophane. The other opening 28 is covered by afluorescent screen 30 which exhibits a green fluorescence underbombardment by radioactive material. Zinc sulphide may be employed asthe fluorescent material, for example, but any suitable screen may beused and the color of the screen when activated is not necessarilygreen. The color of the screen and that of the filter 29 should be thesame, however.

The reference numeral 3! indicates a shutter which is pivoted on theshoulder stud 20 next to the disc I1. One end of the shutter extendsover the fluorescent screen 30 and carries a small disc of radioactivematerial 32 which is in alignment with the opening 28 when the shutteris in the position in which it is shown in Fig. 3. I

The shutter. 3 I has a limited movement determined by the length of thearcuate slot 33. The stud or pin 34 is fixed to the shutter and extendsthrough the slot. The spring '35, a very light spring, is tensionedbetween the stud 34 and a pin 36 fixed to and projecting from the discIT. The spring tends to maintain the shutter in operative position, thatis, the position in which it is shown in the drawing and in which theradioactive material 32 is opposite the opening 28. The cover 21 has apin 31, Fig. 4, for operating the shutter 3|. When the device is to beput away after use, the cover 2| is rotated in a clockwise direction asseen in Fig. 4 as far as it will go. Toward the end of this movement thepin 31 engages the tail 38 of shutter 3| and rotates the shutter onitspivot until the stud 34 reaches the end of the slot 33, where theshutter remains until the device is to be used again. In the oiTposition of the shutter, the radioactive material 32 is displaced fromits operative position over the opening 28 and that portion of thescreen 30 which covers the opening is not subjected to irradiation.

The element 32 may be made of any suitable radioactive material capableof causing fluorescence of the screen 36 and having a long enough halflife so that its decay will not appreciably change the amount of lightemitted by the screen in a reasonable period of time. which has beenused with excellent results is a small disc of silver impregnated withradium. The active substance may also be radium D.

The reference numeral 40 indicates a graduated light transmitting screenor light valve which is secured to the inside of the cover 2| behindwindow 25 in any suitable manner, as by means of cement or otheradhesive. This screen comprises a plurality of sections such as A! and42 of different light transmitting power. There may be, for example, 14sections, of which the first section is substantially transparent whilethe remaining sections are progressively less so in the ratio of 2 to 1.Thus. if the numeral 1600 represents the transparency or lighttransmitting power of the first section, then the transparency of thesecond section. is 800', of the third section, 400, and so on, giving avalue of .2- for the 14th section.

Screens such as 40 maybe made of sensitized film by a process ofprinting from a suitable negative. The negative may be made by layingout the sections on a. piece of film and masking all of the sectionsexcept one section, which is then exposed for a predetermined intervalto a weak light source. The mask is then moved to uncover the secondsection as well as the first section and a second exposure is made. Themask is then moved again to uncover the third section and a thirdexposure. is made, and so on, until the last section has been uncoveredand the last exposure has been made. Thus each exposure takes in onemore section than the immediately preceding exposure. The first sectionis exposed 14 times and comes out nearly opaque when the film isdeveloped. The last section, exposed only once, is nearly transparentand the intermediate sections have varying degrees of transparencycorresponding to the values mentioned in the preceding paragraph. Itwill" be understood that the negative should be so made that in thepositives printed therefrom the order of decreasing transparency of thesections is in the right direction. In the case of the photometer shownin the drawing the direction is clockwise in Fig. 1.

It will be seen that the screen 40 is adapted to function as a lightvalve, adjustable by rotation of the cover 2| to regulate the amount oflight admitted to the opening 2! through the filter 29.

The operation of the photometer will now be described, it being assumed.that a. picture is to An element be taken and that the operator desiresto use the photometer for selecting the stop or exposure time which issuitable for the light condition obtaining. The selection also dependson the film speed and the first step is to note the speed of the film tobe used. The ring [4 is then rotated until the index I6 is opposite thenumeral such as 64 on scale l3 which indicates the speed valueascertained. The ring l4 may remain in this position so long as filmhaving the same speed is used. Some allowance can be made for specialconditions, as indicated by the adjustment shown.

The operator next rotates the cover 2i, Fig. 1, in a counterclockwisedirection far enough to release the shutter 3| to operative position,thereby moving the radioactive material 32 into operative relation tothe fluorescent screen 39, or rather that portion of itwhich covers theopening; 23'. The rotation of the cover also moves one end of thegraduated screen 40 into alignment with the opening 27 covered by thefilter 29.

The operator may now bring the eye piece H to one eye and look throughthe photometer in the direction of the view, that is, toward the objectof which a picture is to be taken, with the result that the openings 21and 28 are seen. The lens I2 enables the eye to focus on these openings,so that the inner opening 28, the one covered by the fluorescent screen30, appears clearly as a green spot. This is due to bombardment of thescreen by alpha particles emitted by the radioactive material 32. Theother opening 21 is also seen as a green spot, due to light receivedfrom outside through the graduated screen 40 and the filter 29, but isbrighter or darker depending on the light condition and on theadjustment of the cover 2|. Assuming a fair amount of light and that thefirst section of the graduated screen 40 is aligned with the opening 21,the outer spot will be the brighter of the two. While looking at thegreen spots the operator proceeds to rotate the cover 2| and thus adjustthe graduated screen 40 until the two spots appear to be of equalbrightness or intensity.

Finally, the operator selects the value of stop or exposure time inaccordance with the kind of picture to be taken and then reads the othervalue by reference to the scales 23 and 15. A distant view, forinstance, must be taken with a small stop, or diaphragm opening, say 22,and reference to the scales shows that the proper exposure time is aboutsecond. Another picture, one which includes a moving object, requires ashort exposure such as second, for which the proper stop, underconditions obtaining, is stop 8. It will be clear that in any case theresult depends on the adjustment of the ring I4 in accordance with thefilm speed and the adjustment of the cover and graduated screen 46 inaccordance with the light condition.

The modification shown in Figs. 5- and 6 may now be described briefly.The photometer is the same except for the method of operativelydissociating the radioactive material and the fiuorescent screen whenthe device is not in use. Whereas in the photometer as shown in Figs. 3and 4 the radioactive material is moved away from the used portion ofthe screen; in the modification of Figs. 5 and 6 the radioactivematerial and screen are always in the same fixed relation to each otherand a guard is provided which is interposed between the radioactivematerial and the screen except when the photometer is in use.

Referring to the drawing, the radioactive material 50 is supported onthe bracket which is secured in suitable manner to the metal disc IT.The guard 52 is pivoted at 53 and is normally maintained in the positionin which it is shown by the spring 54. In this position the curved endof the guard is interposed between the radioactive material 50 and thefluorescent screen 6| and is effective to prevent activation of thefluorescent material.

The operating rod 55 has a cam 56 formed at one end and extendingthrough an opening in the disc ll adjacent the straight end of the guard52. The spring 54 surrounds rod 55 and is compressed between the collar51 and the disc Il' whereby the operating rod 55 is normally maintainedin the position in which it is shown. An extension 58 of the rod 55projects through the body Ill and terminates in a button 60.

When the photometer is about to be held up to the eye to make theadjustment for light value, the operator depresses the button 60 andholds it in depressed position While the adjustment is being made. Theoperation of rod 55 causes the cam 56 to engage the guard 52 and rotateit sufficiently to remove its curved end from between the radioactivematerial 50 and the screen 6|, whereby the screen is illuminated aspreviously described. When the operation is finished, the button 60 isreleased and the guard 52 is again interposed between the radioactivematerial and the screen, where it prevents the gradual destr'uction ofthe screen material which would otherwise take place.

The invention having been described that which is believed to be new andfor which the protection of Letters Patent is desired will be pointedout in the appended claims.

I claim:

1. In a photometer, a generally cup shaped casing having a rotatable capat the open end, an opaque diaphragm in front of said cap, a viewingdevice including a lens mounted in the closed end of the casing andadapted to bring points on said diaphragm in focus in the eye of anobserver, a body of radioactive material in said casing between said capand said diaphragm, means comprising fluorescent material supported onsaid diaphragm and responsive to space bombardment from said body forproducing a light spot of constant intensity visible through saidviewing device, an opening in said diaphragm, means comprising a lightvalve in said end cap independent of said opening and adjustable byrotation of said cap to transmit outside light through the entire areaof said opening to form a second light spot thereat visible through saidviewing device, and a filter interposed in the path of the light passingthrough said opening to make said light spots of the same color.

2. In a photometer, a cylindrical shell molded of plastic material, anopaque diaphragm closing said shell at one end thereof, a viewing deviceincluding a lens at the other end of said shell, a stud or post fixed tosaid diaphragm at the center thereof, a cover member of molded plasticmaterial rotatably mounted on said stud, two off center and radiallyspaced windows in said diaphragm, means including fluorescent materialand radio-active material between said diaphragm and cover member fortransmitting light through the inner said window to exhibit a light spotvisible through said viewing device, a. light valve in said cover memberfor transmitting light through the outer said window to exhibit a secondlight spot visible through said viewing device, said valve beingadjustable by rotation of said cover member to make said light spots ofequal intensity, a ring surrounding said shell and rotatable thereon, ascale on said shell calibrated in accordance with film speeds, an indexon said ring cooperating with said scale, and a pair of cooperatingscales calibrated in accordance with exposure times and stops,respectively, one scale of said pair being carried on said ring and theother scale of said pair being carried on said cover member foradjustment relative to the first scale of the pair by rotation of saidcover member to adjust said light valve.

3. In a photometer, a substantially straight tubular casing, an opaquemember extending across said casing inside thereof and forming apartition, said partition having first and second spaced openingstherein side by side and in the same plane, a device including a lens atone end of said casing for viewing said openings, fluorescent materialcovering the first opening on the side of said partition opposite fromsaid viewingdevice, radioactive material inside said casing causing saidfluorescent material to emit light to thereby illuminate the whole areaof said first opening and cause the same to be visible in said viewingdevice, a filter covering the second said opening and adapted totransmit light of the same color as the light emitted by saidfluorescent material, a graduated light valve at the other end of saidcasing for admitting light to said filter and second opening fromoutside the photometer, and means for adjusting said light valve tocause said openings to be illuminated with equal intensity.

4. In a photometer, a tubular casing, a viewing device mounted at oneend of said casing for use in observing the interior thereof, meansincluding a body of radioactive material and a fluorescent screen insidesaid casing for producing a spot of light of constant intensity in therange of said viewing device, means for producing a second spot of lightalong side said first spot, said last means including a rotatable lightvalve at the other end of said casing for admitting light thereto, saidlight valve having a closed position and a plurality of open positionsin which it admits different amounts of light to said casing, a movablemember supporting said body, said member having a first position inwhich said body is operatively related to said screen and a secondposition in which said body is displaced from said screen sufficient toprevent activation thereof, means operated by rotation of said lightvalve to its closed position to engage and move said member to itssecond position, and means responsive to rotation of said light valve toany open position to restore said member to its first position.

5. In a photometer, a cylindrical housing, an opaque diaphragm closingsaid housing at one end thereof, a viewing device including a lens atthe other end of said housing, a stud or post fixed to said diaphragm atthe center thereof, a cover member rotatably mounted on said stud, twooff center and radially spaced windows in said diaphragm, meansincluding fluorescent material and radio-active material between saiddiaphragm and cover member for transmitting light through the inner saidwindow to exhibit a light spot visible through said viewing device, alight valve in said cover member for transmitting light through theouter said window to exhibit a second light spot visible through saidviewing device, said valve being adjustable by rotation of said covermember to make said light spots of '7 equal intensity, a ringsurrounding said housing and rotatable thereon, elements comprising anindex and a scale calibrated in accordance with film speeds, one of saidelements being carried on said ring and the other being carried on saidhousing, whereby said elements are relatively adjustable by rotation ofsaid ring, and a pair of co- .operating scales calibrated in accordancewith exposure times and stops, respectively, one scale of said pairbeing carried on said ring and the other scale of said pair beingcarried on Said cover member for adjustment relative to the first scaleof the pair by rotation of said cover member to adjust said light valve.

6. In a photometer, a housing, alight standard within the housingcomprising a fluorescent screen and a radioactive element, said screenbeing adapted to emit visible light under exposure to emission from saidradio-active element, an optical device including an eye piece in saidhousing providing a path of observation of said screen presenting animage of the same to a viewer, a light valve for admitting a beam oflight to said housing and directing the same to a position adjacent saidscreen within range of view through said eye piece for comparison withthe light emitted by said screen, said light valve including a membershiftable to vary the intensity of light admitted, said shiftable memberhaving a plurality of active positions and an inactive position, andmeans cooperatively relating said shiftable member and said lightstandard and comprising a member movable in response to movement of saidshiftable member to exclude access to said screen of emission from saidradio-active element when said shiitable member is in inactive position.

7. In a photometer, a housing, a light standard within said housingcomprising two elements of which one element is a fluorescent screenadapted to emit visible light upon exposure to radio-active emission andthe other element is a radio-active body, one of said elements beingmovable between a first position in which said screen is exposed toactivating emission from said body and a second position in which saidscreen is deprived of activating emission from said body, optical meansincluding an eye piece in said housing providing a path of observationof said screen presenting an image of the same '8 and means responsiveto movement of said shiftable member for producing a coordinatedmovement of said movable element to maintain the same in its firstposition when said beam is on and in its second position when said beamis off.

8. In a photometer, a casing, fluorescent material inside said casing,radio-active material inside said casing and operatively related to saidfluorescent material to cause a surface thereof to emit light ofsubstantially constant intensity, a comparison screen of light filteringmaterial mounted in said casing adjacent to and in substantially thesame plane as said light emitting surface, said screen being adapted totransmit light of the same color as that emitted by said surface, anadjustable light valve admitting light from outside said casing toilluminate said. screen, a viewing device including a lens in saidcasing through which said surface and screen may be observed, andinterposed opaque masking means inte cepting all the light transmittedtoward said viewing device from said surface and screen except thattransmitted by predetermined, limited, and sharply defined areas thereofwhich are visible in said viewing device as separate spots of light,said spots being spaced apart a substantial distance by a dark areawhich is continuous with a dark area surrounding both said spots.

9. A photometer as claimed in claim 8, wherein the visible areas are ofsubstantially the same size and are spaced apart a distance not lessthan a major fraction of the smallest dimension'of said areas.

10. A photometer as claimed in claim 8, wherein the visible areas arecircular and of approximately the same size and are spaced apart adistance which is approximately equal to the diarneter of one of saidareas.

GORDON F.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 445,743 Ballard Feb. 3, 18911,351,999 Howenstine Dec. 14, 1920 1,990,022 Du Mend et al. Feb. 5, 19352,074,226 Kunz et al Mar. 16, 1937 2,47 6,340 Wallhausen July 19, 1949FOREIGN PATENTS Number Country Date 214,670 Germany Oct. 18, 1909298,762 Germany June 27, 1917 754,347 France Nov. 6, 1933

